This invention relates to a circuit used to provide I/O signals between a first and a second device. More particularly, this invention relates to a circuit that can be configured to operate in one of multiple modes using a single path extending to the second device. Still more particularly, this invention relates to an I/O circuit in meter electronics of a Coriolis Mass flowmeter that minimizes the number of terminals needed in the meter electronics to support different secondary devices that operate in different modes.
It is known to use Coriolis effect mass flowmeters to measure mass flow and other information of materials flowing through a pipeline as disclosed in U.S. Pat. No. 4,491,025 issued to J. E. Smith, et al. of Jan. 1, 1985 and Re. 31,450 to J. E. Smith of Feb. 11, 1982. These flowmeters have one or more flow tubes of a curved configuration. Each flow tube configuration in a Coriolis mass flowmeter has a set of natural vibration modes, which may be of a simple bending, torsional, radial, or coupled type. Each flow tube is driven to oscillate at resonance in one of these natural modes. The natural vibration modes of the vibrating, material filled systems are defined in part by the combined mass of the flow tubes and the material within the flow tubes. Material flows into the flowmeter from a connected pipeline on the inlet side of the flowmeter. The material is then directed through the flow tube or flow tubes and exits the flowmeter to a pipeline connected on the outlet side.
A driver applies a force to the flow tube. The force causes the flow tube to oscillate. When there is no material flowing through the flowmeter, all points along a flow tube oscillate with an identical phase. As a material begins to flow through the flow tube, Coriolis accelerations cause each point along the flow tube to have a different phase with respect to other points along the flow tube. The phase on the inlet side of the flow tube lags the driver, while the phase on the outlet side leads the driver. Pickoffs are placed at two different points on the flow tube to produce sinusoidal signals representative of the motion of the flow tube at the two points. A phase difference of the two signals received from the pickoffs is calculated in units of time.
The phase difference between the two pickoff signals is proportional to the mass flow rate of the material flowing through the flow tube or flow tubes. The mass flow rate of the material is determined by multiplying the phase difference by a flow calibration factor. This flow calibration factor is determined by material properties and cross sectional properties of the flow tube.
Meter electronics including a processor and connected memory receive the pickoff signals and execute instructions to determine the mass flow rate and other properties of the material flowing through the tube. Th meter electronics can also use the signals to monitor the properties of Coriolis flowmeter components. The meter electronics can then transmit this information to a remote secondary processing device. It is also possible for the meter electronics to receive signals from the remote secondary processing device for the purpose of modifying flowmeter operation. For purposes of the present discussion, a remote secondary processing device is any system capable of receiving signals from and/or transmitting signals to the meters electronics. The actual functions and operation of remote secondary processing devices is not covered in the scope of this invention.
It is a problem in the Coriolis flow meter field in particular and in other fields in general that different types of remote secondary processing devices may be connected to the meter electronics. Each different type of remote secondary processing device may communicate in one of several different modes. Some examples of different modes include but are not limited to digital signaling, 4-20 milliamp analog signaling, active discrete signaling, passive discreet signaling, active frequency signaling, and passive frequency signaling. For each mode supported by the meter electronics or a corresponding electronic device in another field, the meter electronics must have at least one terminal and typically two terminals connected to the circuitry needed to support the mode.
The need for separate circuits for each mode supported by the meter electronics is a problem. If the meter electronics are to be adaptable to provide signals in different modes to support each different mode, an additional circuit must be added for each mode and supported by the meter electronics. Each additional circuit adds to both the material and assembly cost of the meter electronics. Furthermore, unless a specific circuit for a specific mode is added, the specific mode cannot be supported by the meter electronics. There is a need in the Input/Output (I/O) signaling art in general and in the Coriolis flowmeter art in particular for a system that reduces the amount of circuitry in an I/O circuit while maximizing the number of modes supported by the circuitry.
The above and other problems are solved and an advance in the art is achieved through the provision of an I/O signaling circuit that is capable of operating in a plurality of modes while using a single path to transmit signals to and/or receive signals from a remote secondary processing device. This allows each I/O circuit in a device to operate in any one of a plurality of modes which reduces the number of circuits needed to provide I/O signaling between a first and a second device.
An I/O signaling circuit that is capable of operating in a plurality of modes while using a single path through the circuit operates in the following manner. A power supply is connected to a high potential output terminal. A first variable impedance device, such as a transistor, is connected between the high potential output terminal and a low potential output terminal. A second variable impedance device connects the low potential terminal to a ground via a resistor.
The first variable impedance device can be opened or closed to complete a circuit between the high potential and low potential terminals of the I/O circuit to control the voltage between the high potential and low potential terminals. The second variable impedance device controls the flow of current from the power supply, through a remote secondary processing device connected to the high and low terminals to ground. The two variable impedance devices are controlled in the following manner to configure the I/O signaling circuit to operate in a particular mode. A controller executes instructions that determine the mode in which signals are to be transmitted and generates signals that configure the I/O signaling circuit.
The controller generates a first signal that is applied to the first variable impedance device. The first signal causes the first variable impedance device to complete or open a circuit which, in turn, controls the current flowing through the remote secondary processing device from the high potential terminal to the low potential terminal in series with the remote secondary processing device. In the preferred embodiment, the first signal is a digital signal that opens and closes a p-channel MOSFET transistor comprising the first variable impedance device.
A second signal is also generated by the controller. The second signal is applied to a voltage-to-current converter which, in turn, controls the second variable impedance device. The second signal causes the second variable impedance device to control the amount of current that flows through the remote secondary processing device and the series connected second variable impedance device to ground. As the current flows to ground, a resistor connected in series with the second variable impedance device causes a voltage proportional to this current to be fed back to an input of an Operational Amplifier (Op-Amp) and to an Analog to Digital (A/D) converter. The Op-Amp generates a control voltage which is applied to an input of the second variable impedance device to control the current flowing from the power supply, through the remote secondary processing device, through the second variable impedance device and the resistor to ground. The first and second signals are varied by the I/O controller to transmit or receive signals in a desired mode as set out below.
These and other advantages of the present invention will be apparent from the drawings and a reading of the detailed description thereof.